The lack of any threatening competition against the iPad this year has increased at least one analyst’s estimations for overall 2011 tablet shipment numbers.

Analyst Mark Moskowitz of investment bank J.P. Morgan chimes in on the situation:

“Beyond the iPad, there has not been another high-volume tablet offering, yet. We are still awaiting the emergence of a clear number two player, though this may not happen until the launch of Windows 8 in 2H 2012.”

As a result, Moskowitz has raised his initial 2011 tablet shipment prediction to 51.9 million units, up from a previous prediction of 46.1 million. Apple’s market share of the tablet sector is also expected to be higher than initially thought at 70.9 percent with overall tablet revenue as high as $28.9 billion by the end of 2011.

The analyst is expecting a changing playing field in 2012, however, as the big players should have their latest offerings by then. The tablet-optimized Windows 8 OS is anticipated to launch, as well as the yet to be announced Amazon tablet. These two competitors in particular are predicted to put a dent on Apple’s market share down to 62.8 percent, says Moskowitz.